Electronic evaporator



Sept. 20, 1966 R. HAEFER ET AL ELECTRONIC EVAFORATOR 2 Sheets-Sheet 1 Filed May 29, 1963 m vfl I I? ///J &W

. w, m l\ a United States Parent O" 3,274,417 ELECTRONIC EVAPORATOR Ren Haefer, 8483 Kollbrum, Zurich, Switzerland, and Erich Zollinger, 9496 Balzers, Churerstr. 326, Balzers, Liechtenstein Filed May 29, 1963, Ser. No. 284,198 Claims priority, application Switzerland, May 30, 1962, 6,572/ 62 9 Claims. (Cl. 313-75) The invention relates to an electronic evaporator for vacuum coating technology. In the already known electronic evaporators, the substance to be evaporated is surrounded by a spiral-shaped glow cathode and without using .a crucible is exposed to the impinging electrons. Such applications have the advantage of clean evaporation without crucible reactions, but the disadvantage that the substance must be in rod shape and electrically conductive if it is to serve as anode in this arrangement.

In another design of an electronic evaporator the liquid or powdered substance is placed in a graphite crucible or in a crucible made of metal which is surrounded by an incandescent cathode. Heating and evaporating is accomplished here indirectly in that the outer wall of the crucible is heated by electronic bombardment. This process carries with it the risks of undesirable Chemical reactions between substance and crucible wall because the crucible, heated through the outer wall, assumes a temperature higher than that of the evaporation substance. Another known method is to bombard the substance in the crucible with electrons from electron guns arranged directly above the crucible whereby only a small part of the .surface of the substance has to be melted and evaporated. The crucible wall heats up relatively little from the heat conducted from the heating zone, and it has been suggested to melt with an electron gun in several crucibles placed side by side in the evaporator, by the use of a deflection device which directs the electron "beam in quick succession from evaporator crucible to evaporator crucible letting the beam remain shortly on the evaporant in each crucible. However, arrangement with electron guns With `a focused beam are costly because they require electronic-optical precision and careful adjustment while in operation and are quite an obsruction, even if arranged to the side of the vertical crucible axis above the crucible, in :a space which could serve to accommod ate objects to be coated such as lenses, eye-g-lasses, mirror backs, substrat-a for the fabrication of electrical layer-strata resistances. Above all, however, they hinder the use of large, rotatin-g object 'carriers for the objects to be coated :and the utilization of a vapor stream with a large aperture angle.

It is the objective of the invention to utilize the advantages of melting and evaporating electronically and to avoid at the same time the disadvantages just mentioned.

According to the invention the electronic evaporator for evaporation of substances in a high vacuurn has a carrier which is located coaxially with an electron-emitting ring cathode which is different from the prior practices in that the ring cathode is surrounded by a negative auxiliary electrode for the production of an electron ring beam which is directed onto the substance to be evaporated, and also that between the ring cathode and the substance to be evaporated a 'positive accelerator electrode which surrounds the substance to be evaporated is arranged in such a way, that the cathode with respect to the vapor stream emitted from the evaporating substance lies in the shadow of the accelerator electrode.

The invention is described in more detail with the aid of the accompanying drawings wherein FIGURE 1 shows a coater with the electronic evaporator of the invention,

3 ,2 74 ,4 l 7 Patented Sept. 20, 1966 and FIGURE 2 shows an enlarged schematic view of the evaporator shown in FIGURE 1.

Referring now .to the drawings, number 1 is the shell or bell jar of a coater in which the objects to be coated are fastened to a work holding fiXture 2. Number 3 designates the evacuation port', 4 the electronic evaporator in its entirety. The electronic evaporator consists of the carrier 5 which has a trough shaped depression 6 into which the substance to be evaporated, 7, is placed. Carrier 5 is surrounded by the ring shaped cathode 8 (FIGURE 2) which may be brought in a conventional way to the emission temperature. The current lead-ins are vacuum tight and insulated and are lead through the base plate 12 of the coater. Furthermore the cathode 8 is connected with a voltage source via the voltage lead-in 13 so as to be highly negative with respect to the shell or bell jar of the coater and the carrier 5.

Furthermore, a negative auxiliary electrode is provided which serves to deflect the electrons and to focus them on the substance to be evaporated. This auxiliary electrode in the case of this embodiment consists of several parts. Number 15 is a metallic cylinder which has a circular groove 16. The crcular groove 16 and the groove 17 of the upper end of the cylinder 15 are covered by a ring shaped part 18 and the parts 15 and 18 together form a ring shaped hollow electrode which surrounds the ring cathode with an annular cavity 19 directed toward the center. This electrode assumes the same negative potential as the cathode. When in operation, the cathode emits electrons which are directed to the crucible aXis 20 by a positive accelerator electrode. These electrons form a conical electron-ring beam, the tip of which beats the substance to be evaporated. In the accompanying draw-` ing the side wall 9 of the crater shaped trough, which is positive as is the carrier 5 in contrast to the negative cathode, is itself the accelerator electrode surrounding the substance to be evaporated and around which the electronring beam is deflected to such a degree that the cathode 8 lies in the shadow as regards the vapor stream from the substance to be evaporated. Thus cathode '8 is safely protected from coating. It became evident that this arrange ment safely avoids electric gas discharges between the cathode and the grounded structural parts.

Otherwise a zone of high vapor pressure and an ion cloud form under the eiTect of the electron bombardment above the evaporating substance, which results in an electric gas discharge as soon as the vapor cloud touches the cathode. Such a discharge must be -avoided because it leads to the rapid destruction of the cathode. The life span `of the cathode arranged according to the invention, which actually eliminates this discharge, eXceeds many times that of the conventional electronic evaporators where electron source is openly exposed to the vapor source.

In the attached drawing of the invention the cathode 8 is located underneath the upper rim of the wall 9 of the positive accelerat-or electrode which holds the substance to be evaporated. In this case the electrons rise at a slant through cavity 19 and must be deflected or more from their initial direction to hit the substance to be evaporated. An arrangement with a deflection of more than 90 is particularly desirable when the vapor of the evaporating substance is readily ionized and susceptible to electrical discharges.

In addition to the negative auxiliary electrode for generating .an electron ring beam directed onto the substance to be evaporated, means for generating electrical and/or magnetic defiector fields for the adjustment of sharpness and location of the focal point of the electron ring beam may still be used in the generally known manner. As shown in FIGURE 1 for instance, two coils 10 and 11 generate a magnetic deflector field which may be regulated by regulating the current flow in the coils.

The drawings also show provisions for the cooling of the electronic evaporator while in operation. cooling water is admitted into the hollow space of carrier 5 through the partly visible pipeline 21 and is removed through pipeline 22. Cylinder 1=5 may be coo led in the same manner. cooling ring 23 with lead-in 24 (and a discharge pipe located behind it and not visible) serve this purpose. All cooling pipes pass through a vacuurn tight connection 25 in the base plate 12. The insulated current and v-oltage lines f-or the cathode and the negative auxiliary electrode are suitably arranged within the cooling pipes and are, therefore, also cooled at the same time. In this case oi l can be recommended as a coolant, in other cases water is commonly used.

EIGURE 1 portrays schematically the required pump system for -the evacuation of the coater. It usually consists of a multi-stage diflusion pump 26, a mechanical fore pump 26', and lines 27 and 28 with valves 29, 30, 31 and 32 to allow first pre-evacu ation in the known manner by *by-passing the diffusion pump and subsequently to permit Creation of high vacuum by the diffusion pump. Number 33 is an ordinary oil bale. The shell or bell jar of the coater has an observation window at 35.

Results both interesting and very important for the vacuum coating technology were achieved with the new electronic evaporator. For instance, quartz powder which up t-o now could not be evaporated from crucibles without reduction of the low absorbing oxides, may be evaporated ele-ctronica-lly without the slightest oxygen loss and deposited on lenses and mirrors as a completely ab- -sonption free protective coating. As every export in the field of coating technology knows, such ecoatings are of great importance in the production of interference multilayer systems with 20 or more individual layers, because in a case like this the slightest absorption of the individual layers would lead to an intolerable light l oss ot the system.

An example of present application is the production of "cold li gh mirrors. These are in-terference mirrors with approximately 25 alternating highand low-refracting absorpti-on-free layers. "Cold light mirrors are useful by way of example in movie project-ors to obtain maximum picture brightness by reflecting visible light through the film and to eliminate or reduce heating of the film by -transmitting .the infrared light away from the film. It is an important economic .advantage of this invention, that the h ighand low-refracting oxides required for this application and many other similar interference layer applications, may be deposited directly without reduction of the oxides and without additional steps in the process. The electronic evaporator of the invention is a compact unit which can be put int-o any existing coater quickly and without special structural changes, whereas known electron guns for the same purpose require a special installation which often produces Conflict with other parts of the existing coater.

We claim:

1. In an electronic evaporator for the evaporation of substances in a high vacuum:

an anode having an outer end,

a cathode formed in -a substantially regular closed shape to produce an electron beam having a substant-ially closed periphery coaxial with said anode and disposed radially outwardly of said anode and axially inwardly from the outer end of said anode,

an auxiliary electrode surrounding said cathode and formed to limit the initi al direction of electrons emitted from sa-id cathode to angles less than degrees with respect to the axis of said anode, and

means for establishing a potential dierence between said cathode and said anode to defiect said electrons toward the end of said anode.

2. The electronic evaporator of claim 1 wherein the last mentioned means deects the electrons from their initial directions through angles of at least 90 degrees.

3. The electronic evaporator of claim 1 wherein the outer end of said anode is formed with a surface adapted to carry the substances to be evaporated.

4. In an electronic evaporator for the evaporation of substances in a high vacuum:

an anode formed with an outer surface adapted to carry the substance to be evaporated,

a ring cathode coaxial with said anode and disposed radially outwardly of said anode and axially inwardly from said surface of said anode,

an auxiliary electrode surrounding said cathode and formed to limit the initial direction of electrons emitted from said cathode to angles less than 90 degrees with respect to the axisof said anode, and

means for establishing an electric potential difference between said cathode and said anode t-o deflect said electrons from their inital directions to angles of at least 90 degrees toward said surface of said anode.

5. The electronic evaporator of claim 4 wherein the auxiliary electrode is formed with ta radially inwardly extendin g portion to shield said cathode from direct line exposure to vapor flow in the evaporator.

6. The electronic evaporator of claim 4 wherein the auxiliary electrode member has a generally cy lindrieal form with a circular groove `formed therein substantially enclosing said cathode member.

7. The electronic evaporator of claim 4 wherein said electric potential difference `forms a substantially electrostatic field for controlling width and focal point of the cathode emitted electrons.

8. The electronic evaporator of claim 4 having' means for producing a magnetic field tor controlling the area and position of the focal point of the electron beam emitted by said cathode.

9. The electronic evaporator as claimed in claim 6 wherein:

said auxiliary electrode member upper surface forms a cup-shaped contour radially outwardly of and axially `above said cathode member; and

an upper ring member is fixedly connected to said auxiliary electrode member t-o form therewith a ringshaped hollow electrode substantially enclosing the cathode.

References Cited by the Examiner UNITED STATES PATENTS 3,040,l12 6/1962 Smith 13-31 3,132,198 5/1964 Du Bois et al. 13-31 X 3,202,794 8/1965 Shrader et al. 219-121 DAVI'D J. GALVIN, Primary Exam'ne'.

GEORGE N. WESTBY, Exam'ner.

D. E. SRAGOW, Assistant Examiner. 

1. IN AN ELECTRONIC EVAPORATOR FOR THE EVAPORATION OF SUBSTANCES IN A HIGH VACUUM: AN ANODE HAVING AN OUTER END, A CATHODE FORMED IN A SUBSTANTIALLY REGULAR CLOSED SHAPE TO PRODUCE AN ELECTRON BEAM HAVING A SUBSTANTIALLY CLOSED PERIPHERY COAXIAL WITH SAID ANODE AND DISPOSED RADIALLY OUTWARDLY OF SAID ANODE AND AXIALLY INWARDLY FROM THE OUTER END OF SAID ANODE, AN AUXILIARY ELECTRODE SURROUNDING SAID CATHODE AND FORMED TO LIMIT THE INITIAL DIRECTION OF ELECTRONS EMITTED FROM SAID CATHODE TO ANGLES LESS THAN 90 DEGREES WITH RESPECT TO THE AXIS OF SAID ANODE, AND MEANS FOR ESTABLISHING A POTENTIAL DIFFERENCE BETWEEN SAID CATHODE AND SAID ANODE TO DEFLECT SAID ELECTRONS TOWARD THE END OF SAID ANODE. 